Metal gold core

Nano-sized Au particles (>1.5 nm) obtained by evaporation of metallic gold on Mylar [431] exhibit differences in 6 and A q for surface and core atoms when the particle sizes are less than 6 nm. 

Considerable research effort was focused on systems of colloidal gold of which a broad variety of synthetic procedures were reported [140 b, fj. While native colloidal gold solutions are only stable for a restricted time, Brust et al. [141] were able to overcome this problem by developing a simple method for the in situ preparation of alkyl thiol-stabihzed gold nanoparticles. This synthetic route yields air-stable and easy to handle passivated nanoparticles of moderate polydispersity, and is now commonly employed for the preparation of inorganic-organic core-shell composites. Such composites are used as catalytic systems with principally two different functions of the protective 3D-SAM layer. Either the metal nanoparticle core can be used as the catalytically active center and the thiol layer is only used to stabihze the system [142], or the 3D-SAM is used as a Hnker system to chemically attach further catalytic functions [143]. 

These results, taken together, give a strong indication that all the atoms of the gold core of the Aujj cluster compound are already well into the state of metallic binding, i.e. that the valence electrons have become delocalized, and that metallic screening in this system can be considered to be nearly complete. 

Most of the work dealing either with the assembly of metal nanoparticles or with metal nanoparticles as additives in liquid crystals has been carried out using nanoparticles with gold cores. Such gold nanoparticles display unusual and unique size-dependent chemical and physical properties their surface can be passivated in... 

Bimetallic particles with layered structures have opened fascinating prospects for the design of new catalysts. Schmid et al. [10m] have applied the classical seed-growth method [20] to synthesize layered bimetallic Au/Pd and Pd/Au colloids in the size range of 20-56 nm. The sequential reduction of gold salts and palladium salts with sodium citrate allows the gold core to be coated with Pd. This layered bimetallic colloid is stabilized by trisulfonated triphenylphosphane and sodium sulfanilate. More than 90% metal can be isolated in the solid state and is redispersable in water in high concentrations. 

In a different study [40], argon-saturated aqueous solutions of NaAuCT and PdCh or K2PtCl4 were reduced simultaneously by ultrasound irradiation to prepare noble metal alloy nanoparticles. The Au-Pd nanoparticles exhibited mono-dispersive distribution (8 nm), and consisted of a gold core and a palladium shell. Au-Pt alloy nanoparticles could not be produced from NaAuCl4 and K2PtCl4 aqueous solutions by either simultaneous or successive reduction. 

Selvan and coworkers167168 utilized a block copolymer micelle of polystyrene-block-poly(2-vinylpyridine) in toluene exposed to tetrachloroauric acid that was selectively adsorbed by the micelle structure. On exposure of this solution to pyrrole monomer, doped PPy was obtained concurrently with the formation of metallic gold nanoparticles. The product formed consisted of a monodispersed (7-9 nm) gold core surrounded by a PPy shell. Dendritic nanoaggregate structures were also reported... 

We have also examined [78] the conversion of silver cores into the more noble metal gold via oxidation with AUCI4. This process was expected to be quite facile given the rapid kinetics for cyanide oxidation. However the deposition of gold within the core via ... 

FIGURE 5.7 Principle of block copolymer lithography for spatially defined placing of gold nanoparticles on surfaces [16]. (a) Block copolymer stmcture, (b) formation of micelles with a metal ion core, and (c) formation of thin hlms hy dip coating and plasma treatment to remove organic layer. (See insert for color representation of the figure.)... 

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